Solar power was once the choice only of idealists who put the environment before economics; however, production of solar panels is ramping up rapidly and is expected to double in both 2008 and 2009, with growth driven by government support especially in Germany and Japan.
Governments are turning to the sun as a weapon both against climate change and energy dependence. Subsidies are needed because solar is still more expensive than conventional power sources like coal, but costs are dropping by around 5 percent a year and “grid parity,” without subsidies, is already a reality in parts of California.
Grid parity could be achieved sooner by smart management of conventional solar systems. In a conventional solar array, all of the individual panels in the array must receive full sunlight for the array to work properly. If a portion of the array is shaded or otherwise impaired, the entire array power output—even from those sections still exposed to sunlight—is lowered. Inevitably, efficiency-killing variations among panels exist in the vast majority of solar arrays. When these variations go undetected and uncorrected the result is that a significant amount of energy, and money, is “left on the roof.”
High-resolution monitoring devices and diagnostic tools are needed to extract better performance from solar arrays. A solar array may comprise tens, hundreds or even thousands of individual panels. If data could be collected from each of those panels it could be used to optimize the power output of the entire array over its lifetime. The ability to maintain an array at maximum power efficiency significantly increases its energy generation potential.
What is needed is a way to identify panels with differing voltage characteristics during array operation. Knowledge of the voltage output of individual panels would be valuable to owners and operators of solar arrays because it would allow them to identify which panels were dragging down the efficiency of their solar power systems.
In this application, solar “cells” are monolithic semiconductor devices that generate electric current when light shines on them. Cells are connected to other cells through both series and parallel electrical connections. A “string of cells” is a set of cells connected electrically in series. A “panel” comprises strings of cells connected electrically in parallel. A “string of panels” is a set of panels connected electrically in series. An “array” comprises strings of panels connected electrically in parallel. Finally a collection of arrays forms a “site”.
Conventional solar panel junction boxes lack the capability to monitor system performance at the panel level. In conventional systems only the overall performance of an array, or even a site, is measured.